Energetics of Half-Quantum Vortices

Magnetic cantilever measurements have detected half-flux states in mesoscopic rings of the layered material Sr2RuO4, adding evidence that superconducting Sr2RuO4 may be described by a p-wave order parameter. A proposal accounting for this behavior has been presented in which the polarization axis of the condensates lies entirely in the plane. In a half-flux state there is a non-zero polarization, due purely to kinematic effects, which couples to an in-plane magnetic field, lowering the half-flux state's free energy. The viability of such a model and a determination of phenomenological parameters depends heavily on the specific geometry used. A set of Ginzburg-Landau equations has been solved using COMSOL and geometries very similar to the experimental set-up. The results show that the Ginzburg-Landau model can qualitatively reproduce the experimental data within the physically allowable parameter space.